**3. Conclusions**

*Banana Nutrition - Function and Processing Kinetics*

*2.4.5 Glass transition on shrinkage in convective drying*

wellness' [115, 117–119].

to provide improved banana safety and quality. Nonthermal processing has been found to facilitate the development of innovative banana products. Nonthermal technologies have been used to decontaminate, pasteurize and produce commercial sterilization of some banana products with good quality and excellent nutrient retention. The most important priority for future food science research will be the demand by consumers for technologies to meet consumer expectations with optimum-quality safe-processed banana. Zhang et al. [113] listed priorities and factors to consider when conducting research into novel nonthermal and thermal technologies for quality safe banana products as target microorganisms to provide safety, target enzymes to extend quality shelf life, maximization of potential synergistic effects, alteration of quality attributes, engineering aspects, reliability and economics of technologies and consumer perception of banana products from these technologies. They are of the opinion that the new technologies 'to process foods should be driven at maximizing safety, quality, convenience, costs, and consumer

Several methods are employed for the preservation of banana products; drying is one of them. Drying is a heat and mass transfer process which removes moisture and thereby reduces the water activity of the banana products through vapourization or sublimation, which minimize enzymatic and microbiological reactions within the banana products. Several researchers have worked on drying and drying rate of different food materials. The drying rate has been found to depend on factors that influence the transfer mechanisms, such as the vapour pressure of the material and of the drying air, the temperature and air velocity, water diffusion in

Shrinkage of dried banana products is an important change in the physical state of the product during drying which affects the quality of the final material, producing large alterations in its volume. This phenomenon during drying is affected by glass transition. According to Roos [121], glass transition temperature (Tg) is the temperature at which an amorphous system changes from the glassy to the rubbery state. According to him in the glassy state, molecular mobility is extremely slow, due to the high viscosity of the matrix. Thus, the Tg can be taken as a reference parameter to characterize properties, quality, stability and safety of dried banana products [122]. Mayor and Sereno [123] and Bhandari and Howes [124] found that at most drying conditions, a significant amount of the dried product remains in the amorphous state, mainly due to insufficient time for crystallization to occur at the given drying condition. They observed that at rubbery state, shrinkage almost entirely compensates for moisture loss and changes in material volume are equal to the volume of removed water. However, it was observed that in food systems, shrinkage is rarely negligible, and it is advisable to take it into account when predicting moisture

the material, the thickness and surface exposed for drying [120, 121].

content profiles in the material undergoing dehydration [125–127].

*2.4.6 Optimization of drying conditions of bananas in tray dryer using response* 

Drying of banana products involves mass transfer phenomenon. Volume reduction or shrinkage occurs simultaneously during drying process, and it is an undesirable phenomenon in dried products. In general, reduction in volume is due to moisture transfer from dried banana products. This could be as a result of heat transfer into banana slices and mass transfer from the inside to the surroundings thereby causing unfavourable changes in dimensions and shape of the dried products [128, 129].

**76**

*surface methodology*

This chapter showed that moisture content of banana fruits at harvest time is too high for storage and needs to be reduced. Drying characteristics, quality and mass transfer parameters for drying of banana slices were explained, and the process was discussed. It has been found that higher values of effective moisture diffusivity will accelerate moisture velocity within banana slices to achieve removal of moisture from produce for equilibrium moisture content at specific relative humidity. This will help in designing an effective drying method that will save time and energy consumption as well as cost to get good quality products. It was explained that Suzuki's model could be used to explain shrinkage during hot air drying process for banana slices. Shrinkage is a phenomenon and a significant alteration to be considered on quality of dried banana in food engineering applications. The use of this approach will be valuable to select proper drying conditions in order to obtain good quality dried banana products.
